Engineering

Publication Search Results

Now showing 1 - 10 of 180

  • (2009) Carley, J.T.; Rayner, D.S.
    Report



  • (2009) Forbes, Gareth Llewellyn; Randall, Robert Bond
    Conference Paper
    The non-intrusive measurement of the condition of blades within a gas turbine would be a significant aid in the maintenance and continued operation of these engines. Online condition monitoring of the blade health by non-contact measurement methods is the ambition of most techniques. The current dominant method uses proximity probes to measure blade arrival time for subsequent monitoring. It has recently been proposed however, that measurement of the turbine casing vibration response could provide a means of blade condition monitoring, and even give the prospect of providing an estimation of the blade modal parameters. The casing vibration is believed to be excited pre-dominantly by (i) the moving pressure waveform around each blade throughout its motion and (ii) the moments applied by the stationary stator blades. Any changes to the pressure profile around the rotating blades, due to their vibration, will in turn affect these two dominant excitation forces, such that there will be some correlation between the casing response and blade vibrations. Previous work has introduced an analytical model of a gas turbine casing, and simulated pressure signal, associated with the rotating blades. The effect of individual rotor blade vibrations has been developed in order to understand the complex relationship between these excitation forces. A simplified turbine test rig has been constructed. Various aspects of the previous analytical modelling are presented, and then investigated and verified using results from the experimental program with this simplified test rig.


  • (2009) Forbes, Gareth Llewellyn; Randall, Robert Bond
    Conference Paper
    The non-intrusive measurement of blade condition within a gas turbine would be a significant aid in the maintenance and continued operation of these engines. Online condition monitoring of the blade health by non-contact measurement methods is obviously the ambition of most techniques, with a number of methods proposed, investigated and employed for such measurement. The current dominant method uses proximity probes to measure blade arrival time for subsequent processing. It has been recently proposed however, that measurement of the turbine casing vibration response could provide a means of blade condition monitoring. The casing vibration is believed to be excited pre-dominantly by (i) the moving pressure waveform around each blade throughout its motion and (ii) the moments applied by the stationary stator blades. Any changes to the pressure profile around the rotating blades, due to their vibration, will therefore in turn affect these excitation forces. Previous work has introduced an analytical model of a gas turbine casing, and simulated pressure signal associated with the rotating blades. The model has been extended in this paper to more closely represent a commercial gas turbine with experimental verification being presented for various aspects of the analytical modelling procedure.

  • (2009) Russell, Carol
    Journal Article
    There are hopes that new learning technologies will help to transform university learning and teaching into a more engaging experience for 21st century students. But since 2000 the changes in campus university teaching have been more limited than expected. I have drawn on ideas from organizational change management research to investigate why this is happening in one particular campus university context. My study examines the strategies of individual lecturers for adopting e-learning within their disciplinary, departmental and university work environments; to develop a conceptual framework for analysing university learning and teaching as a complex adaptive system. This conceptual framework links the processes through which university teaching changes, the resulting forms of learning activity and the learning technologies used - all within the organizational context of the university. The framework suggests that systemic transformation of a university's learning and teaching requires coordinated change across activities that have traditionally been managed separately in campus universities. Without such coordination, established ways of organising learning and teaching will reassert themselves, as support staff and lecturers seek to optimise their own work locally. The conceptual framework could inform strategies for realising the full benefits of new learning technologies in other campus universities.

  • (2009) Hawkes, Evatt; Sankaran, Ramanan; Chen, Jacqueline; Kasier, Sebastian; Frank, Jonathan
    Journal Article
    The difficulty of experimental measurements of the scalar dissipation rate in turbulent flames has required researchers to estimate the true three-dimensional (3D) scalar dissipation rate from one-dimensional (1D) or two-dimensional (2D) gradient measurements. In doing so, some relationship must be assumed between the true values and their lower dimensional approximations. We develop these relationships by assuming a form for the statistics of the gradient vector orientation, which enables several new results to be obtained and the true 3D scalar dissipation PDF to be reconstructed from the lower-dimensional approximations. We use direct numerical simulations (DNS) of turbulent plane jet flames to examine the orientation statistics, and verify our assumptions and final results. We develop and validate new theoretical relationships between the lower-dimensional and true moments of the scalar dissipation PDF assuming a log-normal true PDF. We compare PDFs reconstructed from lower-dimensional gradient projections with the true values and find an excellent agreement for a 2D simulated measurement and also for a 1D simulated measurement perpendicular to the mean flow variations. Comparisons of PDFs of thermal dissipation from DNS with those obtained via reconstruction from 2D experimental measurements show a very close match, indicating this PDF is not unique to a particular flame configuration. We develop a technique to reconstruct the joint PDF of the scalar dissipation and any other scalar, such as chemical species or temperature. Reconstructed conditional means of the hydroxyl mass fraction are compared with the true values and an excellent agreement is obtained.

  • (2009) Thiruvaran, T; Nosratighods, M; Ambikairajah, E; Epps, J
    Journal Article
    Recently, subband frame-averaged frequency modulation (FM) as a complementary feature to amplitude-based features for several speech based classification problems including speaker recognition has shown promise. One problem with using FM extraction in practical implementations is computational complexity. Proposed is a computationally efficient method to estimate the frame-averaged FM component in a novel manner, using zero crossing counts and the zero crossing counts of the differentiated signal. FM components, extracted from subband speech signals using the proposed method, form a feature vector. Speaker recognition experiments conducted on the NIST 2008 telephone database show that the proposed method successfully augments mel frequency cepstrum coefficients (MFCCs) to improve performance, obtaining 17% relative reductions in equal error rates when compared with an MFCC-based system.